ECE321 Electronics I Fall 2006 Professor James E. Morris Lecture - - PDF document

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ECE321 Electronics I

Fall 2006 Professor James E. Morris

Lecture 12 2nd November, 2006

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Bipolar Junction Transistors (BJTs)

5.3 Amplifiers & Switches (Basic circuits) 5.4 DC Circuits

(Biasing)

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Figure 5.26 (a) Basic common-emitter amplifier circuit. (b) Transfer characteristic of the circuit in (a). The amplifier is biased at a point Q, and a small voltage signal vi is superimposed on the dc bias voltage VBE. The resulting output signal vo appears superimposed on the dc collector voltage

• VCE. The amplitude of vo is larger than that of vi by the voltage gain Av.

Figure 5.27 Circuit whose operation is to be analyzed graphically.

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Figure 5.28 Graphical construction for the determination of the dc base current in the circuit of Fig. 5.27. Figure 5.29 Graphical construction for determining the dc collector current IC and the collector-to-emitter voltage VCE in the circuit of Fig. 5.27.

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Figure 5.30 Graphical determination of the signal components vbe, ib, ic, and vce when a signal component vi is superimposed on the dc voltage VBB (see Fig. 5.27). Figure 5.31 Effect of bias-point location on allowable signal swing: Load-line A results in bias point QA with a corresponding VCE which is too close to VCC and thus limits the positive swing of vCE. At the other extreme, load-line B results in an operating point too close to the saturation region, thus limiting the negative swing of vCE.

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Figure 5.32 A simple circuit used to illustrate the different modes of operation of the BJT. Figure 5.34 Analysis of the circuit for Example 5.4: (a) circuit; (b) circuit redrawn to remind the reader of the convention used in this book to show connections to the power supply; (c) analysis with the steps numbered.

• Fig. for Ex. D5.22

Find max VBB for BJT active mode α = 1

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Figure 5.35 Analysis of the circuit for Example 5.5. Note that the circled numbers indicate the order of the analysis steps.

• Fig. for Ex. 5.24

Find VB for saturation with βforced = 5

Figure 5.36 Example 5.6: (a) circuit; (b) analysis with the order of the analysis steps indicated by circled numbers.

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Figure 5.37 Example 5.7: (a) circuit; (b) analysis with the steps indicated by circled numbers. Figure 5.38 Example 5.8: (a) circuit; (b) analysis with the steps indicated by the circled numbers.

Figure for Exercise D5.27: β = 50 to 150 Find RC for all circuits in active mode. Find VC range for β = 50 to 150.

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Figure 5.40 Circuits for Example 5.10.

• Fig. for Ex. 5.28

Example 5.10 calculates IC=1.28mA for β=100 Recalculate for β=50 What is % change?

Figure 5.41 Circuits for Example 5.11.

Figure for Exercise 5.29: Find total current from power supply and power dissipation in the circuit. (See Example 5.11)